1. Field of the Invention
The present invention relates generally to operation of multiple display devices with a single computer over a single cable, and more specifically, to selective updating of multiple display devices.
2. Description of the Related Art
The components of a computer system (such as PCs, minicomputers and mainframes) may be divided into two functional units—a computing system and a human interface (or “HI”) to the computing system. For a PC, the computing system may be the CPU, memory, hard drive, power supply and similar components. The computing system may be comprised in a chassis which holds the motherboard, power supply, hard drive and the like. The computer system may also be implemented in other forms, such as a blade computer as described in U.S. Pat. No. 6,012,101 entitled “Computer Network Having Commonly Located Computer Systems”, or U.S. patent application Ser. No. 09/728,667 entitled “Computer On A Card With A remote Human Interface” filed Dec. 1, 2000. The human interface, on the other hand, may comprise those devices that humans use to transfer information to and/or receive information from the computing system. The most commonly recognized devices which form part of the human interface with the computing system include the monitor, keyboard, mouse and printer. The human interface may also include a variety of other devices, such as a joystick, trackball, touchpad, microphone, speakers, and telephone, as well as other devices too numerous to specifically mention.
Increasingly, HIs for computer systems include multiple monitors for presenting large amounts of information to a user. For example, financial or stock analysis workstations typically include at least two monitors to display various tables, graphs, documents, and program interfaces to the analyst. Generally, this is accomplished through the use of multiple (usually two) video cards in the computer, although there are some video cards which support two independent video outputs. Drawbacks to this approach include the cost of providing multiple video cards (or special video cards with multiple outputs) for the computer system, as well as the limitation on the number of monitors supported (usually two or three), due to the limited number of slots and/or buses available on the computer.
In most multi-display computer systems, e.g., current PC architectures, the human interface (e.g., the display monitor, mouse, and keyboard, etc.) is closely located to the computer system, by a distance typically less than about 10 to 15 feet. This distance constraint severely limits the placement of the multiple video monitors in a system, and thus, limits the usability and flexibility of the system. In some current multi-display computer systems, the operational distance from the computer to the video displays has been extended, e.g., by converting digital video signals to analog signals for propagation over distances up to ˜100 feet, and by using compensation amplifiers in the case of longer cable runs.
However, current approaches to extended multiple monitor computer systems require individual cables for each monitor. In other words, current approaches include a hub which connects to the computer, and which has multiple outputs for connecting with respective multiple monitors via respective multiple cables. Thus, if the computer system includes four monitors at the HI location, then four separate cables must be run from the hub to the displays, increasing the expense of the system.
Additionally, in the installation of cabling, the cost of pulling the cable, e.g., through walls, ceilings, etc., may greatly exceed the cost of the cable, and so the use of multiple cables to connect the monitors may involve substantial expense. These problems may be illustrated more clearly by FIG. 1 and its associated text.
FIG. 1—Computer System With Multiple Display Devices (Prior Art)
FIG. 1 illustrates a computer system which supports multiple display devices, i.e., computer monitors, according to the prior art. As FIG. 1 shows, in the prior art approach, a computer 102 is coupled to a hub 111, e.g., via a cable 104. The hub 111, in turn, is coupled to a plurality of computer displays, i.e., computer monitors 108A–108D via respective cables 104A–104D. Multiplexed video signals, and optionally, I/O device signals, are sent from the computer 108 to the hub 111, where the multiplexed video signals are separated and routed over the appropriate cables 104 to respective monitors 108. Thus, as FIG. 1 shows, the prior art approach necessitates that multiple cables (e.g., 104A–104D) be run from the hub 111 to distribute the video signals. In this prior art approach, the hub 111 receives a single large video frame or image, and partitions the frame into a plurality of sub-frames, each of which constitutes a frame or image for a respective monitor. The processing involved in decomposing the single large frame into the respective sub-frames may require complex processing and may greatly limit the flexibility of the system regarding changes in configuration of the system, e.g., addition or subtraction of monitors from the system, changes in resolution of the images, etc.
The parallel couplings between the hub 111 and the monitors 108 may also require substantially more cable than a single monitor system. As was mentioned above, generally, the cost of running the cable exceeds that of the cable itself, thus, the use of multiple parallel cables to couple the monitors to the hub may involve significant expense, in that in some embodiments, each of the cables 104A–104D may have to be “pulled” through walls, floors, etc., during installation of the system.
In one approach to supplying content for display to multiple monitors, as disclosed in U.S. patent application Ser. No. 10/198,719 titled “Connecting Multiple Monitors To A Computer Using A Single Cable”, filed Jul. 7, 2002, whose inventor is Barry Thornton, video frames are multiplexed and sequentially sent to the monitors on a single cable. Each monitor (or a respective frame-grabber coupled to the monitor) selects and records the frame or image it is to display. This frame or image is then played back to the monitor at a refresh rate appropriate to that monitor. However, in this process the actual refresh rate of the data may be considerably slower than the refresh rate of the frame to the associated monitor. Thus, the cursor location on the screen that is displaying the cursor is generally updated at a slower rate than in the case where a single monitor is used. In other words, because the video frames are multiplexed, the image data is consequently updated less frequently than in a single monitor system, possibly resulting in poor performance or responsiveness from the user's perspective.
Thus, improved systems and methods for updating a display in a multi-display system are desired.